This invention relates to fluid energy dissipation devices and in particular to a fluid pressure reduction device with a plurality of stacked disks securely maintained by mechanical fasteners in an assembled condition.
In the control of fluid in industrial processes, such as oil and gas pipeline systems, chemical processes, etc., it is often necessary to reduce the pressure of a fluid. Adjustable flow restriction devices such as flow control valves and fluid regulators and other fixed fluid restriction devices such as diffusers, silencers, and other back pressure devices are utilized for this task. The purpose of the fluid control valve and/or other fluid restricting device in a given application may be to control flow rate or other process variables, but the restriction induces a pressure reduction inherently as a by-product of its flow control function.
Currently there is available an assembly of a plurality of stacked disks forming a fluid pressure reduction device fused together in a brazing process with additional mechanical fasteners added if desired to securely maintain the stacked disks assembled in a cage assembly. The cage assembly may be inserted into a fluid control valve to receive a valve control member, such as a plug, movable through the hollow center of the cage assembly.
As an example, in U.S. Pat. No. 6,026,859, assigned to the same assignee as herein, a plurality of stacked disks in a cage assembly include alternating flow disks and plenum disks with hollow centers. Respective cage ends are provided on opposite ends of the stacked disks. One of the cage ends includes a series of threaded bores and the opposite cage end includes a corresponding number of countersunk bores. A corresponding number of holes are drilled, cut or punched through each disk so that in the assembled stacked disks configuration, each disk hole can be aligned with a respective threaded bore in one cage end and with a respective countersunk bore in the opposite cage end. In the final assembly, the disks are maintained together by welding or brazing along the outer diameter of the assembled disks. Alternatively, a threaded bolt is inserted through the one cage end and through the disks to threadably engage the threaded bore in the opposite cage end.
In an improved embodiment, the stacked disks include two cage end members one of which has a series of tapered bores. A taper nut is inserted into and engageably contacts the corresponding tapered bore so that tightening of the bolt and nut mechanically secures the stacked disk-cage assembly.
In the usage of such devices, it has been found that the sliding motion of the plug through the inner cage undesirably wears down the inner diameter of the cage assembly and causes undesirable galling between the inside diameter cage surfaces and the plug outer surface.
It is therefore desired to provide wear resistance and galling protection for these devices in use.
In accordance with the principles of the present invention, there is provided a fluid pressure reduction device with guide members formed of a hard metal within the cage inner perimeter for guiding a valve control member, such as a plug movable through the cage inner perimeter for reducing wear and galling on the inner perimeter.
A fluid pressure reduction device according to the invention includes a plurality of stacked disks having an outer perimeter and an inner perimeter defined by a hollow center aligned along a longitudinal axis and forming a cage assembly of the stacked disks, A plurality of longitudinal channels are formed in the stacked disks around the inner perimeter. Guide members formed of a metal harder than the disks are provided in each longitudinal channel, with the dimensions of the guide member in the longitudinal channel cooperating so that the guide member substantially conforms to the dimensions of the cage inner perimeter.
The guide members form a guide at the cage inner perimeter for the valve control plug member moving through the cage assembly go an to reduce wear and galling by the valve control member on the inner perimeter of the cage assembly.
In a preferred embodiment of the invention, the guide members comprise longitudinal rods of a hard/wear resistant material, such as ULTIMET (R) Alloy or Alloy 6, the guide rod material being harder or at least having greater wear resistant characteristics than the disk material and sufficient to prevent galling and wear damage with its adjacent sliding member. The rods are adapted in the longitudinal channels so that the outer surface of the rods substantially match and conform to the inner perimeter of the cage assembly. Accordingly, the valve control plug outer surface will be guided by the outer surfaces of the guide rods as the plug moves through the cage inner perimeter.
Alternatively, longitudinal weld bead strips can be deposited within the longitudinal channels to comprise the guide members. The longitudinal weld bead strips can be formed of a hardfacing material, such as ULTIMET (R) Alloy or Alloy 6, and are located within the channels so that the exposed surface of the bead strips substantially matches and conforms to the inner perimeter of the cage assembly.